The inclusions as particles of separate phases suspended in a liquid metal can be classified into two types, hard inclusions and soft inclusions. Hard inclusions are oxides or other non-deformable particles, such as aluminum oxide, magnesium oxide, silicon oxide, aluminum carbide, silicon carbide, titanium diboride and vanadium diboride. Soft inclusions are attributable to gas bubbles, molten slag, molten salt droplets, and agglomerates of other very small particles or other deformable inclusions. Examples of soft inclusions include chloride types which come from degassing processes using chlorine or chloride or fluxing molten metal. Soft inclusions also come from using granular salts in a furnace. Inclusions cause pinholes in foil and container sheets such as food, can sheets or beverage can sheets and are also involved with breakage of wire during drawing operations and surface defects such as streaking in automobile trim. Inclusions also serve as nucleating sites during solidification and thereby affect the stress and fatigue life of certain products.
Comparing relative harm to the quantity of a liquid metal, the gas bubbles might be less harmful than that of the hard inclusion since they generate less stress and do not nucleate as easily. Moreover, the gas bubbles can be eliminated in process treatment. The gas bubbles might form the pseudo signal similar to that of a hard particle, causing the measurement results to overestimate the inclusion concentration in the liquid metal and consequently influence the measurement accuracy of a resistive pulse technique. Therefore, it is necessary to discriminate gas bubbles from hard inclusions for high gas containing or gas sensing liquid metal or alloy when using a resistive pulse technique.
Currently, the inclusions in metal that are analyzed and classified are attributable to destructive testing and non-destructive testing. The destructive testing involves the following methods. Using a microscope, solid metal samples can help to determine qualitatively and semi-quantitatively whether an inclusion is a hard inclusion or a soft inclusion. Metallographical analysis is used to analyze the inclusions in a metal that are concentrated in a sample by passing the molten metal through a filter to search for the inclusions at the leading edge of the filter. Porous disc filtration analysis (PoDFA™) and liquid aluminum inclusion sampler (LAIS™) are two commercially available sampling systems based on metallographic analysis. Metallographic analysis provides semi-quantitative analysis, identifies the inclusion types and distinguishes between hard inclusions and soft inclusions, but does not give results in real time. Ultrasonic non-destructive testing is another method that performs an analysis only on metal in a solid state, however, it cannot identify whether an inclusion originated as a hard inclusion or a soft inclusion.
A current instrument used for measuring inclusion concentrations employs a Coulter counter as a liquid stream that passes through a flow through cell. A Coulter counter is a testing technique used for counting pulses in a liquid stream that passes through a flow through cell. The measurement principle involves measuring a voltage pulse when the inclusions pass though an electric sensing-zone by inserting a pair of electrodes inside and outside of a small flow through cell. As inclusion particles flow through this flow through cell and as the voltage between the electrodes increase, the electric sensor produces voltage pulses. The voltage pulses have amplitudes which are a function of the effective particle diameter.
Means are needed to discriminate and classify or identify the two different types of inclusions in a liquid metal stream in real time to determine the original size of soft inclusions and to identify the soft inclusion types according to their deformable behaviors. These factors influence the signal from surface tension forces that drive a free particle toward a spherical shape, whereas initial conditions and/or fluid-dynamic forces are the primary sources of forming a non-spherical shape. The method for distinguishing, classifying and measuring soft and hard inclusions in liquid metal show that the fluid-dynamic forces come from the pressure gradient due to variation of the shaped-wall and the self-induced Lorentz forces. The variation of deformation and volume shrinkage affect the drag of any bubbles and the transit time of the bubbles. passing through the flow through cell will consequently change which will be reflected on the voltage pulse measurement.
It is an object of the present invention to provide a method to discriminate and identify different types of inclusions in a liquid metal stream in real time.
It is an object of the present invention to provide a method that produces sizing information for both hard and soft inclusions according to a prototype voltage signal.
It is another object of the present invention to provide a method to identify the degree of softness for soft inclusions to discriminate gas bubbles and slag according to their deformable behaviors.
What is really needed is a method for distinguishing, classifying and measuring soft and hard inclusions in liquid metal that discriminates and identifies different types of inclusions in a liquid metal stream in real time, that provides sizing information for both hard and soft inclusions according to a prototype voltage signal and identifies the degree of softness for soft inclusions to discriminate gas bubbles and slag according to their deformable behaviors.
These and other objects of the present invention will become apparent from reference to the figures of the drawings and the detailed description which follow.